Ira L. Fedder

Osteogenic protein versus autologous interbody arthrodesis in the sheep thoracic spine : a comparative endoscopic study using the Bagby and Kuslich interbody fusion device

STUDY DESIGN Using an in vivo interbody arthrodesis model, the efficacy of the Bagby and Kuslich (BAK) device packed with recombinant human osteogenic protein-1 (rhOP-1) was evaluated. OBJECTIVES To compare the efficacy of osteogenic protein with that of autograft for interbody arthrodesis, with fusion success based on biomechanical, histologic, and radiographic analyses. SUMMARY OF BACKGROUND DATA The use of recombinant human bone morphogenetic proteins (rhBMPs) as osteoinductive bone graft substitutes or expanders has recently gained considerable research interest, particularly when applied in posterolateral arthrodesis. However, whether these results can be extrapolated to a successful interbody spinal arthrodesis remains uncertain. METHODS Twelve sheep underwent a multilevel thoracic spinal decompression by thoracoscopic approach. Three noncontiguous destabilization sites (T5-T6, T7-T8, T9-T10) were prepared and randomly treated as follows. Control group treatments were nonsurgical, destabilization alone, and empty BAK. Experimental groups were treated with autograft alone, BAK device packed with autograft, or BAK device packed with rhOP-1. Four months after surgery, interbody fusion status was quantified by biomechanical testing, computed tomography, microradiography, and histomorphometry. RESULTS Results of biomechanical analysis showed statistically higher segmental stiffness levels when comparing the control and experimental groups with four of the five testing methods (P < 0.05). Computed tomography and microradiography characterized destabilization alone as producing one fusion in six preparations; the empty BAK, two in six;, autograft alone, four in eight; BAK with autograft, five in eight; and BAK with rhOP-1 group, six in eight-all evidenced by woven trabecular bone spanning the fusion sites. Histomorphometry yielded significantly more trabecular bone formation at the fusion sites in the three experimental groups than in the two control groups (P < 0.05). CONCLUSIONS Interbody spinal fusions showing biomechanical and histomorphometric equivalency to autologous fusions have been achieved with rhOP-1. The functional unit stability and histologic osteointegration evidenced by the BAK/rhOP-1 complex shows this interbody arthrodesis technique to be a viable alternative toconventional autologous iliac crest, thereby obviating the need for an iliac crest donor site and associated patient morbidity.

Revisability of the CHARITE artificial disc replacement: analysis of 688 patients enrolled in the U.S. IDE study of the CHARITE Artificial Disc.

Study Design. A prospective, randomized, multicenter, FDA-regulated Investigational Device Exemption clinical trial. Objectives. To analyze the incidence of, and reasons for, reoperation in all patients (treatment and control) enrolled in the IDE study. Summary of Background Data. This is the first report of the incidence and nature of reoperations following lumbar TDR as part of a controlled, prospective, multicenter trial. Methods. A total of 688 patients meeting the inclusion and exclusion criteria were enrolled in one of three arms of the study at 14 centers across the United States. This cohort includes 71 nonrandomized cases, 205 randomized cases, and 313 continued access cases, all receiving the CHARITÉ Artificial Disc, as well as 99 randomized cases in the control group (ALIF with threaded fusion cages and autograft). A detailed analysis was performed of clinical chart notes, operative notes, and adverse event reports for all patients requiring reoperation following their index surgery. Results. Of the 589 patients with TDR, 52 (8.8%) required reoperation. Of the 99 patients with lumbar fusion, 10 (10.1%) required reoperation, and an additional 2 required surgery for adjacent level disease (P = 0.7401). There were 24 TDR patients who underwent a repeated anterior retroperitoneal approach, with 22 (91.7%) having had a successful removal of the prosthesis. Seven of the 24 TDR prostheses requiring removal were revised to another CHARITÉ Artificial Disc. The mean time to reoperation in all patients was 9.7 months. A total of 29 patients (4.9%) in the TDR group required posterior instrumentation and fusion as did 10 (10.1%) in the control group (P = 0.0562). At 2 years or more follow-up, 93.9%(553/589 = 93.9%) of patients receiving TDR with the CHARITÉ Artificial Disc had a successfully functioning prosthesis with a mean of over 7° of flexion-extension mobility. Conclusions. Lumbar TDR with the CHARITÉ Artificial Disc did not preclude any further procedures at the index level during primary insertion, with nearly one third being revisable to a new motion-preserving prosthesis and just over two thirds being successfully converted to ALIF and/ or posterior pedicle screw arthrodesis, the original alternative procedure.

Revision Strategies for Salvaging or Improving Failed Cylindrical Cages

STUDY DESIGN This is a review of 20 patients who experienced failure of threaded interbody fusion cages and underwent surgical correction. OBJECTIVE To review the causes and possible treatment strategies for failed cylindrical cages. SUMMARY OF BACKGROUND DATA Intraoperative complications have been described in the past; however, management of the postoperative patient with failure of interbody fusion devices has not been described. METHODS In 20 patients with failed threaded titanium fusion cages (18 Bagby and Kuslich Devices [BAK; Sulzer-Spine Tech, Minneapolis, MN], 2 Ray Threaded Fusion Cages [Ray TFC; Surgical Dynamics, Norwalk, CT) who underwent revision surgery, all had failure before successful arthrodesis was achieved. Eight of the original titanium cages had been inserted anteriorly (7 laparoscopically), and 12 had been inserted for posterior interbody lumbar fusion. Before the revision surgery, five of the implants were thought to be solid by the referring surgeon, but pseudarthrosis was clearly present in all. In addition, 14 other explanted BAK devices were subjected to undecalcified histologic preparation, quantitative histomorphometry, and histopathologic analysis. RESULTS The average length of time before revision surgery (implant duration) was 31.8 weeks (range, 1-156 weeks). The most common revision procedure was posterior exploration of the symptomatic nerve root with foraminotomy for unrecognized lateral recess stenosis (11 cases) or excision of iatrogenically herniated intervertebral disc fragments (4 cases). However, four cages inserted through posterior exposure during an interbody lumbar fusion procedure had to be removed because of migration into the spinal canal. In nine cases posterior pedicle screw instrumentation was necessary in addition to posterolateral fusion using iliac crest bone grafting. CONCLUSIONS All 20 cages failed because of surgical technique rather than an intrinsic defect in fusion cage technology. The factors associated with failure of the original insertion procedure were failure to achieve adequate distraction of the anulus fibrosis; undersized cages, especially when placed through the posterior interbody lumbar fusion approach; cerebrospinal fluid leakage or pseudomeningocele; Type 2 diabetes mellitus; the use of local bone graft rather than iliac crest inside the cage; anterior insertion in an excessively lateral position resulting in symptoms of a far lateral disc herniation; and failure to identify the spinal midline during an anterior approach.

Video-assisted thoracoscopic surgery versus open thoracotomy for anterior thoracic spinal fusion. A comparative radiographic, biomechanical, and histologic analysis in a sheep model.

Study Design. In this in vivo investigation, a sheep model was used to compare the efficacy of a video‐assisted thoracoscopic approach and a traditional thoracotomy in promoting a successful interbody spinal arthrodesis. Objectives. To compare the incidence of successful anterior spinal arthrodesis among three stabilization techniques‐iliac crest, Bagby and Kuslich device, and Z‐Plate‐performed using a video‐assisted thoracoscopic approach and conventional open thoracotomy approaches. Summary of Background Data. A clinical outcome study on open versus endoscopic spinal fusion is not yet available. Moreover, no basic scientific investigations have been conducted to determine whether the success of an endoscopic arthrodesis is comparable to that of a conventional open procedure. Methods. Fourteen Western Crossbred sheep underwent three identical destabilization procedures at T5‐T6, T7‐T8, and T9‐T10, in which the anterior and middle osteoligamentous columns of the spine were resected, followed by three randomized reconstruction procedures using iliac autograft alone, Bagby and Kuslich device packed with iliac autograft, and Z‐plate stabilization with iliac autograft. In seven sheep, the entire destabilization‐reconstruction procedure was performed using a video‐assisted thoracoscopic surgical approach. In the remaining seven, the procedure was performed by conventional open thoracotomy. Results. Histomorphometric and biomechanical evaluation demonstrated that the video‐assisted thoracoscopic approach and open thoracotomy arthrodesis had comparable bone formation and biomechanical properties (P > 0.05). However, the Z‐plate fusions, as a group, demonstrated increased flexion‐extension stiffness properties and trabecular bone formation compared with the autograft and Bagby and Kuslich device fusions (P < 0.05). Conclusions. Thoracic interbody spinal fusions performed by thoracoscopy have demonstrated histologic, biomechanical, and radiographic equivalence to those performed by a thoracotomy approach. However, in the endoscopy group, intraoperative complications causing longer operative times, higher estimated blood loss, and increased animal morbidity indicated a substantial learning curve associated with the adoption of this surgical technique.

Analysis of porous ingrowth in intervertebral disc prostheses: a nonhuman primate model.

Study Design. A study was conducted to investigate the biomechanical, histochemical, and biologic ingrowth characteristics of the most widely used total disc prosthesis, the hydroxyapatite-coated SB Charité prosthesis. Objective. To compare the porous ingrowth, linear apposition, or bony ingrowth in total disc replacement with published reports of porous ingrowth prostheses in the appendicular skeleton. Methods. Seven mature baboons (Papio cynocephalus) underwent L5–L6 total disc replacement through an anterior transperitoneal approach. The SB Charité prosthetic vertebral endplates (n = 14) were cobalt-chrome covered by two layers of thin titanium with a hydroxyapatite coating, which was electrochemically bonded to the implant surface. Results. At 6 months after surgery, the range of motion exhibited by the SB Charité and the nonoperative control subjects under axial compression, flexion–extension, and lateral bending showed no statistical difference (P > 0.05). Plain film radiographic analysis showed no lucencies or loosening of any prosthetic vertebral endplate. Gross histopathologic analysis of the hydroxyapatite-coated SB Charité prosthesis demonstrated excellent ingrowth at the level of the implant–bone interface, without evidence of fibrous tissue or synovium. Histochemical assays showed no accumulation of particulate wear debris (no titanium, ultrahigh molecular weight polyethylene, or cobalt-chrome) nor cytokines (tumor necrosis factor-&agr;, prostaglandin E2, interleukin-1, -2, or -6). Total endplate area showed a mean ingrowth (volume fraction) of 47.9% ± 9.12% and a total ingrowth range of 35.5% to 58.8%. Conclusions. The porous ingrowth (percentage of pore ingrowth coverage at the bone–metal interface) was more favorable for total disc replacement than for cementless total joint components in the appendicular skeleton (range, 10–30%). The reason for the improved degree of porous ingrowth in total disc replacement prostheses probably is that ligamentotaxis causes sustained compression across the metal–bone interface.

Experimental design of total disk replacement-experience with a prospective randomized study of the SB Charitè.

Study Design. Prospective randomized clinical trial. Objectives. To determine if a prospective randomized study of patients with symptomatic degenerative disc disease treated with disc arthroplasty could be safely completed. Methods. Sixty patients with one-level discogenic pain confirmed by plain radiography, magnetic resonance imaging, and provocative discography for degenerative disc disease were randomized comparing 1/3 BAK anterior interbody fusion and 2/3 anterior SB Charitè artificial disc replacement. Results. The mean age was 40.3 years (range 21–56 years). Nineteen cases were at L4–L5 and 41 cases were at L5–S1. Nineteen cases had BAK anterior interbody fusion and 41 cases were randomized as SB Charitè disc replacement. The length of surgery was mean 88.4 minutes (range 54–137 minutes) for both groups. The estimated blood loss was mean 289.5 cc (range 50–1800 cc). The length of hospital stay was a mean of 3.03 days (range 2 to 6 days). Oswestry Disability Index for the BAK control group was 45.9 ± 10.4 before surgery and 23.5 ± 17.2 at follow-up (P < 0.001). The corresponding ODI scores for the SB Charitè disc were 50.0 ± 14.3 before surgery and 25.0 ± 20.1 at a mean of 2 years’ follow-up (P < 0.001). Conclusions. This is the first study that shows improvement of functional outcome measures in a prospective randomized design treating primarily mechanical back pain and achieving comparable successful results to lumbar spinal stenosis decompression.

Distribution of in vivo and in vitro range of motion following 1-level arthroplasty with the CHARITÉ artificial disc compared with fusion

OBJECT One of the goals of lumbar arthroplasty is to restore and maintain range of motion (ROM) and to protect adjacent levels from abnormal motion, which may be a factor in transition syndrome following arthrodesis. In this study, in vitro ROM results were compared with in vivo, 2-year postoperative radiographic ROM evaluations. METHODS Radiographs of patients enrolled in the CHARITE investigational device exemption study were analyzed at baseline and at 2 years postoperatively. The ROM in flexion/extension at the implanted and adjacent levels was measured, normalized, and compared with ROM results obtained using cadaver (in vitro) evaluations. RESULTS Preoperative ROM distributions in patients enrolled for arthroplasty or fusion at the L4-5 level was as follows: 28% motion was observed at L3-4, 35% at L4-5 and 37% at L5-S1. Following a one-level arthroplasty at L4-5, the in vivo ROM distribution from L-3 to S-1 at the 2-year time point was 36% at L3-4, 30% at L4-5 and 35% at L5-S1. Following a one-level fusion with BAK and pedicle screws at L4-5, the in vivo ROM distribution from L-3 to S-1 at the 2-year time point was 45% at L3-4, 9% at L4-5 and 46% at L5-S1. CONCLUSIONS The baseline as well as the 2-year in vivo data confirmed previously published in vitro data. One-level arthroplasty was shown herein to replicate the normal distribution of motion of the intact spine.

Anterior Bak Instrumentation and Fusion: Complete Versus Partial Discectomy

Beginning in January 1994, a prospective, clinical study was done comparing the effectiveness of complete anterior (Group 1) versus partial reamed channel discectomies (Group 2) in 100 consecutive patients who had anterior BAK instrumentation and fusion using autogenous iliac crest bone graft. At 2 or more years of followup, all patients in Group 1 who had complete operative disc removal achieved solid arthrodesis. There were no revision surgeries. However, in Group 2, there were seven patients who had a pseudarthrosis and an additional patient with early postoperative cage displacement, which resulted in eight patients in Group 2 requiring revision surgery. The differences in operative preparation of the disc space for BAK instrumentation surgery resulting in complications proved to be significant. The use of interbody titanium cages dramatically increases the biomechanical efficacy of anterior fusions. Original proponents of cages advocated removing a cylindrical channel of disc material using a drill. A prospective review of 100 patients who had complete versus partial discectomy revealed 14% of patients in Group 2 eventually had a pseudarthrosis develop.

100 Consecutive Cases of Degenerative Lumbar Conditions Using a Non-Threaded Locking Screw System With a 90-Degree Locking Cap

Background This prospective study analyzes the perioperative outcomes and long-term fusion success of 100 consecutive lumbar degenerative cases. The cases were managed using a non-threaded locking screw system, in conjunction with polyetheretherketone (PEEK) cages, for posterior lumbar interbody fusion (PLIF) procedures. These 100 cases were compared to another prospective study treating patients with the same inclusion and exclusion criteria using conventional plate-based pedicle screw spinal instrumentation augmented with carbon fiber interbody cages. Methods A total of 167 operative levels were treated in 100 patients (51 single-level, 39 two-level and 10 three-level cases). Eleven cases were revisions and 67 patients received interbody fusion cages. Patients had an average of 22.8 ± 4.0 months followup. Results: There was one instrumentation failure but no significant subsidence at the interbody fusion level. The disc space height was restored as part of the surgical procedure at the interbody cage levels: from 7.5 ± 2.3 mm preoperative to 9.0 ± 2.1 mm postoperative. There were 2 cases of pseudarthrosis (2 / 100 = 2%). The average operative time for 1-level cases was 111 ± 25 minutes; for 2-level cases it was 132.4 ± 21.8 minutes; and for 3-level cases it was 162.6 ± 33 minutes. Blood loss averaged 800 ± 473 cc for 1-level cases, 1055 ± 408 cc for 2 levels, and 1155 ± 714 cc for 3 levels. The length of stay was similar between the 3 groups (4.4 ± 1.2 days for single-level cases, 4.7 ± 1.1 for 2 levels, and 5.0 ± 1.1 for 3 levels; P > .05). There were 3 incidental durotomies, and 4 other patients developed infections postoperatively that required reoperation. Conclusion The disc and foraminal heights can be restored and maintained with a unilateral cage and pedicle screw construct. Unilateral transforaminal lumbar interbody fusion using a PEEK cage combined with a non-threaded locking pedicle screw and rod system results in similar fusion rates to those achieved using the bilateral Brantigan interbody fusion cage or a single BAK Vista implant. When compared to the bilateral Brantigan cages, decreased operative time (P < .001), decreased blood loss (P < .001) and reduced incidence of dural tears (P < .001) are advantages of using a non-threaded locking screw system and single PEEK interbody cage for lumbar degenerative conditions without compromising subsequent fusion rates.